Glass containers are often composed of so-called soda-lime glass, also called soda-lime-silica glass. Many such containers are colored, for example, for aesthetic or functional purposes. Colored glass containers may be produced from soda-lime glass compositions which include one or more colorants. For example, blue glass containers can be made from soda-lime glass compositions which include cobalt oxide (CoO) as a colorant. U.S. Patents that illustrate colored glass compositions of this type include U.S. Pat. Nos. 3,326,702, 3,330,638, 3,345,190, 3,498,806, and 4,312,953.
Some colorants in soda-lime glass do not immediately impart color to the glass. Instead, color may need to be developed in the colorant-containing glass by a heat-treatment process known as “striking.” In this process, glass containers are formed from a glass composition which contains “latent” colorants. Thereafter, the glass containers are heated to a temperature slightly above normal annealing temperatures so that the latent colorants in the glass interact or “strike” to impart color to the glass. U.S. Patents that illustrate this method of coloring glass containers include U.S. Pat. Nos. 2,672,423, 3,513,003, and/or 3,627,548.
A general object, in accordance with one aspect of the disclosure, is to provide a glass composition that may be used to produce cobalt blue glass containers that, upon heat treatment and striking, develop a visually black color. Accordingly, this glass composition and the glass containers formed therefrom may be referred to as “black-strikable.” The glass containers may be inspected—before or after striking—by infrared inspection equipment in a glass container production line or in a container filling operation. Accordingly, these glass containers also may be referred to as “inspectable.” Until now, the optical inspection of black glass containers had been thought impossible due to their low percentage of light transmission.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
In accordance with an aspect of the disclosure, there is provided a method of making a black-strikable glass container. In this method, a black-strikable glass composition is prepared having a base glass portion and a latent colorant portion. The base glass portion includes: 60-75 wt. % SiO2, 7-15 wt. % Na2O, 6-12 wt. % CaO, 0.1-3.0 wt. % Al2O3, 0.0-2.0 wt. % MgO, 0.0-2.0 wt. % K2O, 0.01-0.25 wt. % SO3, 0.01-0.25 wt. % Fe2O3, and 0.01-0.15 wt. % CoO. The latent colorant portion includes: 0.0875-0.35 wt. % cuprous oxide (Cu2O), 0.06-0.5 wt. % stannous oxide (SnO), 0.006-0.05 wt. % bismuth oxide (Bi2O3), and 0.02-0.10 wt. % carbon (C). Thereafter, a black-strikable glass container is formed from the black-strikable glass composition.
In accordance with another aspect of the disclosure, there is provided a method of inspecting a black glass container for commercial variations that affect optical characteristics of the glass container. In this method, infrared light energy is directed onto and through the black glass container, and is received on an infrared light sensor. The infrared light sensor is responsive to infrared light energy received thereon having wavelengths in the range of 750-1100 nm.